aocpp/2022/02.cpp

#include <algorithm>
#include <cstdint>
#include <iostream>
#include <numeric>
#include <sstream>
#include <stdexcept>
#include <string>
#include <tuple>
#include <vector>

#include <doctest.h>

#include <aocpp/Startup.hpp>

namespace {

enum class ABC {
  A, B, C
};

enum class XYZ {
  X, Y, Z
};

auto xyzScore(XYZ xyz) -> std::int64_t
{
  switch (xyz) {
    case XYZ::X: return 1;
    case XYZ::Y: return 2;
    case XYZ::Z: return 3;
  }
}

auto outcome(ABC abc, XYZ xyz) -> std::int64_t
{
  switch (abc) {
    case ABC::A:
      switch (xyz) {
        case XYZ::X: return 3;
        case XYZ::Y: return 6;
        case XYZ::Z: return 0;
      }
    case ABC::B:
      switch (xyz) {
        case XYZ::X: return 0;
        case XYZ::Y: return 3;
        case XYZ::Z: return 6;
      }
    case ABC::C:
      switch (xyz) {
        case XYZ::X: return 6;
        case XYZ::Y: return 0;
        case XYZ::Z: return 3;
      }
  }
}

auto DesiredOutcome(XYZ xyz) -> std::int64_t
{
  switch (xyz) {
    case XYZ::X: return 0;
    case XYZ::Y: return 3;
    case XYZ::Z: return 6;
  }
}

auto Pick(ABC abc, XYZ xyz) -> XYZ
{
  for (auto result : {XYZ::X, XYZ::Y, XYZ::Z}) {
    if (outcome(abc, result) == DesiredOutcome(xyz)) {
      return result;
    }
  }
  throw std::runtime_error{"Pick couldn't find result"};
}

using Input = std::vector<std::pair<ABC, XYZ>>;

auto Parse(std::istream & in) -> Input
{
  Input result;
  std::string abc, xyz;

  while (in >> abc >> xyz) {
    result.emplace_back(
      abc == "A" ? ABC::A :
      abc == "B" ? ABC::B :
                   ABC::C,
      xyz == "X" ? XYZ::X :
      xyz == "Y" ? XYZ::Y :
                   XYZ::Z
    );
  }

  return result;
}

auto Part1(Input const& input) -> std::int64_t
{
  return std::transform_reduce(
    input.begin(), input.end(),
    std::int64_t{0},
    std::plus(),
    [](auto x) {
      auto [abc, xyz] = x;
      return outcome(abc, xyz) + xyzScore(xyz);
    });
}

auto Part2(Input const& input) -> std::int64_t
{
  return std::transform_reduce(
    input.begin(), input.end(),
    std::int64_t{0},
    std::plus(),
    [](auto x) {
      auto [abc, xyz] = x;
      xyz = Pick(abc, xyz);
      return outcome(abc, xyz) + xyzScore(xyz);
    });
}

} // namespace

TEST_SUITE("2022-02 examples") {
  TEST_CASE("example") {
    std::istringstream in {
R"(A Y
B X
C Z
)"
    };
    auto const input = Parse(in);
    CHECK(Part1(input) == 15);
    CHECK(Part2(input) == 12);
  }
}

auto Main(std::istream & in, std::ostream & out) -> void
{
  auto const input {Parse(in)} ;
  out << "Part 1: " << Part1(input) << std::endl;
  out << "Part 2: " << Part2(input) << std::endl;
}